The long-term objective of this proposal is to learn the role of cytoskeletal alterations in the degeneration of neurons in normal aged and Alzheimer disease, a major public health problem in modern society with its rapidly increasing elderly population. The two most prominent lesions in aged especially Alzheimer disease brain are the presence of numerous intraneuronal argentophilic fibrillary tangles of paired helical filaments (PHF) and the neuritic (senile) plaques which too contain bundles of PHF in their neurites. PHF are morphologically unlike any of the normal neurofibers, their origin and role in the disease are not understood. The microtubule associated protein tau is a major component of the PHF. Tau both in PHF and in unpolymerized form is abnormally phosphorylated. It therefore appears that modification of tau, either phosphorylation alone or in conjunction with other modifications yet to be identified might be a factor in cytoskeletal pathology and the formation of the PHF. To elucidate the role of altered tau in the cytoskeletal pathology, studies will be undertaken to 1) isolate normal tau and the unpolymerized abnormally phosphorylated tau to homogeneity, 2) generate peptides and localize the sequence/s containing the abnormal phosphorylation, the phosphorylation sites of normal tau and identify the amino acid/s which is abnormally phosphorylated, 3) raise and characterize monoclonal and polyclonal antibodies to the abnormal tau and to the tau fragment/s containing the abnormal epitope and isolate abnormal tau by immunoaffinity using these antibodies, and 4) study the in vitro polymerization of the abnormal tau. Establishment of the exact nature of the chemical alteration of tau in aging and AD/SDAT will be a major step towards elucidating the origin of PHF and its role in neuronal degeneration. The development of the specific immunological probes, i.e., antibodies will not only help achieve the above objective but will also be very valuable for future studies on the development of a possible laboratory diagnostic test for cytoskeletal pathology in affected brain by direct immunoassays of CSF and possibly serum.